Uniform asphalt pavement and production method therefore

ABSTRACT

A uniform asphalt pavement of substantial area composed of aggregates of varying natural qualities produced by a systematic process including mix design, mix analysis, and plant control methods. A volumetric comparison is mathematically made between blendings of coarse and fine aggregates defined over a single sieve size and a Riguez Index to determine voidage in the compacted aggregate mixture. The Riguez Index is characteristic to the particular fine aggregates used in the blending. For controlling voidage at the mixing plant, the respective quantities of coarse and fine aggregates injected into the mixing plant is controlled over the same single sieve size used for demarcating coarse and fine aggregates in mathematically computing the volumetric comparison. Further, a stability function derived from different combinations of crushed fine and blend sand, and a flexibility function derived from different mix quantities of asphalt cement provide control of flexibility and stability values.

CROSS-REFERENCES TO RELATED APPLICATIONS AND PATENTS

This invention is a continuation-in-part of allowed U.S. applicationSer. No. 023,390 filed Mar. 23, 1979 entitled MIX DESIGN METHOD FORASPHALT PAVING MIXTURES by the same inventor hereof, now U.S. Pat. No.4,221,603, which is a continuation-in-part of Ser. No. 764,336, filedJan. 29, 1977, now abandoned.

This invention is related to U.S. application Ser. No. 123,206 entitledASPHALT PAVEMENT MIXING PLANT WITH PLURAL WEIGHT CELLS filed Feb. 21,1980 by the same inventor hereof.

This invention is related to U.S. application Ser. No. 123,205 entitledUNSEGREGATOR SHROUD FOR HOT-MIX ASPHALT LAY-DOWN MACHINE filed Feb. 21,1980 by the same inventor hereof.

BACKGROUND OF THE INVENTION

This invention concerns asphalt pavements. It also concerns systematicprocedure for mix design, mix analysis, and job control for producing auniform asphalt pavement of substantial length having uniform physicalproperties.

In the plant-mix type pavement construction, a road bed and/or subgradeon which an asphaltic concrete mixture is laid generally are prepared bygrading, compacting, and leveling. The asphaltic mixture is prepared ata remote plant site and is transported to the prepared road bed. Themixture is then dumped in place, spread by a paving machine, and finallycompacted in place by heavy steam rollers.

Plant-mix production consumes large quantities of materials, typicallyas much as 6000 tons per day, thus possibly depleting any given singleaggregate source, such as a rock quarry, sand pit, or other source ofmineral deposits. Aggregate materials of pavements of several miles ormore generally are gathered from several sources and accordinglynonuniform pavements result from source variations. Furthermore duringthe initiation of a production run, several miles of pavement typicallyare laid before the materials engineer has acquired sufficient knowledgeof the aggregate qualities to establish consistent physical propertiesin the pavement. In many cases, consistent qualities may never beachieved either because the production job is completed before thematerial engineer has had the opportunity to correct for sourcevariations, or the nature and quality of the aggregate changes toorapidly for the materials testing engineer to perform required tests anddetermine appropriate corrective action at the mixing plant. In manycases, the aggregate source intentionally is changed to shorten thedistance between the aggregate source and the mixing plant whereuponattempts are then made to bring the new mixture within jobspecifications.

At the mixing plant, the amount of asphalt cement injected into themixing bin can be reasonably accurately controlled as a percentage byweight of the total mix. Effective asphalt cement governs the amount ofair voids in the compacted mixture and varies as a function of theirshape, absorption characteristics, and sizes. Attempts are made toregulate size by controlling gradation over a multitude of screen sizes,generally 8 to 10, ranging from coarse aggregates passing the 1" screendown to mineral filler passing the No. 200 screen. Gradation however isalmost impossible to control the job mix formula at the mixing plant andat the lay-down site due to degradation and segregation of aggregates.Plant control in accordance with changes in absorption characteristics,aggregate shapes, or other natural qualities are at best based upontrial-and-error techniques.

No method previously exists for quickly measuring changes in the naturalaggregate qualities at the mixing plant site to effect corrective actionat the mixing plant during operation. Further, no method previouslyexists for quickly and accurately determining the necessary correctiveaction for effecting such proper control of the production plant at theplant site. Thus uniform asphalt pavements cannot be produced.

Frictional qualities also are difficult to achieve for dense gradedmixes. An open graded overlay is now used for friction overlays.Frictional qualities are provided by the sharpe edges of 1/2" to 1"coarse aggregate particles protruding upwardly of the riding surface.The asphalt cement in the present open graded frictional overlay ispermeable to water and air penetration causing the cement to ageprematurely resulting in deterioration of the pavement structure. Theunderlying surface of the friction overlay also deteriorates for thesame reasons. One problem associated with attempts to lay dense gradedfriction courses is that the coarse rock is pushed down into theunderlying asphalt pavement upon load application on the riding surfaceand thus frictional qualities disappear. Thus to reduce the effects ofdisplacement and reorientation of aggregate particles, the presentfriction overlay is laid very open graded.

The design of optimum asphaltic mixture today is at best atrial-and-error procedure. Good mixes generally result from knowledge ofaggregates, experience, and luck. Many limitations in achieving optimumpavement properties exist, even with the expert design engineer usingknown aggregates. With some aggregates, present techniques cannot beused to determine a mix design that meets job specifications, such asstability, flexibility, density, or voidage.

In an effort to produce uniform pavements, firstly mix design isperformed by trial-and-error methods to determine what aggregateblendings asphalt cement combination will produce certain predesignatedpavement qualities such as flexibility, stability, and air voidage; andsecondly, crushing, mixing, and laydown operations are controlled toproduce an asphalt pavement having the desired physical properties. Theobject is to produce a pavement so that the load is transmitted to thesubgrade only through the rock while the mortar of fine aggegate andcement fill the intersticies between the rock. The aggregates areproportioned according to a predesignated job mix formula whichcomprises prescribed proportions of different sized aggregates generallyranging from a maximum size of one and one-half inch in diameter to aminimum aggregate size that passes the No. 200 sieve.

Two methods now in general use for mix design and quality testing arethe Marshall and the Heevm methods. According to these methods, testspecimens are prepared by compacting trial mixes within the limitationsof predesignated job mix formula tolerances, and then tested in aneffort to determine which blend possesses desired physical properties,such as flexibility, flowability, density, stability, etc. Thisprocedure consumes as much time as two to three weeks. It must berepeated when the natural qualities of the aggregates change during theproduction operation or when different degrees of segregation anddegradation of aggregates occur during stockpiling, transporting andhandling.

An asphalt pavement containing a large amount of air voids is an "opengraded mix". It is vulnerable to deterioration due to water seepagethroughout the pavement. Water weakens the binding effect of the asphaltcement by stripping the cement from the surface of the aggregates. Anopen graded mix also is subject to aeration which shortens the pavementlife due to oxidation of the asphalt cement. Aeration decreases theviscosity of the cement, causing it to become brittle and ultimatebreakup of the pavement. Where prolonged road life is not important, anopen graded mix, within certain limits, however is used to produce ahigh friction riding surface. Road pliability having resilientcharacteristics is sacrificed in open graded mixes.

The nature of the coarse aggregates determine, among other things, theload bearing and riding characteristics of the pavement. Specificqualities of concern include hardness, shape, porosity, and othersurface qualities. Coarse aggregate may consists of crushed rock,volcanic rock, hydraulically tumbled stoned, or other large mineraldeposits.

A pavement having a small amount of air voids is known as a "densegraded mix". This mixture has a larger quantity of the fineaggregate/cement mortar. Present dense graded mixtures have poorstability and deform under load forces as the coarse aggregates do notproperly transmit loads to the subgrade. Where load conditions permit,pavements comprising dense graded mixes are used when high pliability isdesired.

A maximum "bulking point" is defined herein as the proportion(percentage by weight of dry coarse aggregate with respect to totalweight of dry aggregate in mixture) at which each coarse aggregateparticle touches one another while the mortar of fine aggregate andasphalt cement fill all interstitices between the coarse aggregate. Thegradation at which the bulking point occurs essentially depends on theshape of the coarse aggregate. For example, the available volume ofspace between contiguous hydraulically tumbled stone is different thanthe available volume between contiguous crushed rock, and thus a mixtureincluding one type of coarse aggregate may have a different bulkingpoint than a mixture of another type of coarse aggregate. A mix at orabove the bulking point mixture generally is unacceptable because itlacks, among other things, sufficient flexibility, and resistence to airand water penetration. Some presently specified job mix formulascompletely ignore bulking point limitations in the specification.

A "balance point" is defined herein as the gradation at which eachcoarse aggregate particle are in close proximity to one another whilethe mortar of fine aggregate, asphalt cement, and desired dispersed airvoids fill all interstitices between the coarse aggregate. There shouldbe just enough asphalt cement in the mixture to cover the surfaces ofall aggregates in the mixture, and just enough air voids to allow forproper expansion and contraction of the pavement under the climaticconditions without penetration of excessive water and air. Thus the airvoids are the separating factor between dense and open graded mixesbelow the bulking point. Excessive asphalt cement reduces stability andtoo little asphalt cement generally reduces flexibility. The voidagecontrol is difficult to achieve and maintain during the mixing operationbecause of myriad variables, some of which have been previouslyindicated, and accordingly, uniform pavements cannot be produced bypresent techniques.

At least one procedure presently in use for designing a mixture whichhas the desired quantity of air voids is the manipulation of the job mixformula of discrete sized aggregates over the entire gradation scale.Specifically, Fuller Maximum Density Curves and the Federal HighwayAdministration 0.45 Power Gradation Chart currently are in use. Theiruse is described in "Mix Design Methods for Asphaltic Concrete and otherHot-Mix Type" published by The Asphalt Institute, manual series No. 2,fourth edition, March, 1974. The basis for the FHA 0.45 power gradationchart is described in detail in volume 31, pages 176 through 207 of the"Proceedings of the Association of Asphalt Paving Technologist", Jan.29, 1962. The theory of controlling voidage is based on the principlethat a gradation deviating from a maximum density curve will containincreased air voids. Thus some obscure relationship between job mixformula and voidage is developed for job control. It is rarelysuccessful particularly in view of segregation and degradation ofaggregates while being handled and transported to and from the crushingplant, stock piles, mixing plant, and laydown site. Degradation betweenthe crushing plant and the mixing plant alone may amount to as much as30%.

Another method for computing voids in the mineral aggregate is disclosedin volume 34, pages 574 through 594 of the "Proceedings of theAssociation of Asphalt Paving Technologist". The computations are basedupon successive correlations of voids in discrete ranges of thegradation spectrum. Page 577 of the treatise illustrates 8 gradationranges between mineral filler and 3/8 to 3/4 inch aggregate. By summingthe voidage contained in each aggregate group, and considering thecorrelation factors of aggregate voidage, a sum total is obtained whichclosely approximates the final aggregate voidage. No clue however isgiven to how one might achieve this ideal combination of aggregatemixture at the mixing plant nor is any consideration given to variationin effective asphalt cement.

In any job, the use of local indigenous materials is desired, if at allpossible, because of expensive transportation cost in transportingaggregates across the country. Certain jobs however do not lendthemselves to the use of such indigenous materials because of widelyvarying changes in natural aggregate qualities that render mixing plantcontrol almost impossible. In that case, materials are imported from adistant source.

SUMMARY OF THE INVENTION

In view of the foregoing, it is one objective to provide a uniformasphalt pavement of substantial area which pavement is produced fromaggregates of varying natural quality.

It is another objective of this invention to provide an in situ plantcontrol method for controlling gradation of the mixture thereby toproduce a uniform ashpalt pavement.

It is another objective of the invention to provide a systematic mixdesign and plant control method for producing a uniform pavement havingpredetermined physical properties such as flexibility, flowability,stability, workability, voids in mineral aggregates, voids filled,density, and air voids.

In accordance with this invention, a uniform asphalt pavement ofsubstantial area having a substantially constant volume of effective airvoids under a standard compaction is produced by a systematic procedureof mix design, mix analysis, and plant control to compensate forvariations in specific gravity, particle shape, absorption, sizedistribution, or consolidation of the aggregates that comprise thepavement. To achieve mix design: firstly, the aggregates are demarcatedthereby to define coarse and fine aggregates; secondly, an Indexquantity is derived that represents the quantity of fine aggregateparticles that is contained in a unit volume of the bulk fine aggregatecompacted under the standard compaction, such as the compactive effortdefined by the Marshall method; and thirdly, a proportion of coarse andfine aggregate are selected wherein the mathematiacally computedquantity of fine aggregate per unit of the combined volumes V_(FA) andV_(EAC) substantially equals the Index quantity according to thevolumetric relationship:

    V.sub.CA +V.sub.FA +V.sub.EAC +V.sub.EA =1 unit volume

where V_(CA) is the volume of the coarse aggregate, V_(FA) is the volumeof the fine aggregate, V_(EAC) is the volume of the effective asphaltcement, and V_(EA) is the volume of the desired effective air voidsunder the standard compaction. Plant control is achieved during themixing process by periodically selecting a proportion according to themix design process and adjusting the proportioning controls of the plantto said selected proportion thereby to maintain the desired air voidvolume V_(EA), and thus produce a substantial area of uniform asphaltpavement having a constant or controlled volume of air voids. Mixanalysis is performed on production outputs of the mixing plant toassure proper proportioning. Standard compaction can be performed by theMarshall method, or by a similar compacting method that consolidates thefine aggregates to their upper limits of consolidation. Coarse and fineaggregates may be demarcated by the No. 4 or similar size aggregatesieve. A friction overlay also is produced by this method.

A further aspect of this invention comprises a systematic procedure fordetermining the flexibility stability indexes of an asphalt pavementmixture by varying the quantity of asphalt cement and crushed fineaggregates in the mixture.

The advantages of this invention include the ability to produce uniformpavements of substantial area, reduction of testing procedures and time,and reduction of cost of design and construction. More importantly, myasphalt pavements, can have a useful life exceeding 20-25 years, asopposed to six months to five years for present asphalt pavements.

Because an analysis of any mixture of aggregates can be made by thisinvention, aggregate material from existing pavements already in placecan be crushed and recycled to produce new pavements thereby obviatingthe need to excavate and transport aggregate material from a distantsource.

Further, pavements of both high flexibility (12 to 16) and highstability (2000 psi to 3000 psi) not otherwise achievable can now beproduced with exceptional frictional qualities. Such asphalt pavementscan provide long-lasting safer operation of asphalt concrete airportsrunways and highways than conventional portland cement runways andhighways with friction gratings.

These and other aspects and advantages of the invention will becomereadily apparent upon review of the succeeding disclosure taken inconnection with the accompanying drawings. The invention however ispointed out with particularity in the appended claims.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts volumetric relations of the aggregate blend as a functionof gradation.

FIG. 2 depicts an enlargement of a section of the chart of FIG. 1 thatis useful for job control at the mixing plant, mix design, or analysispurposes.

FIG. 3 depicts the density of aggregates of FIG. 2 as a function ofgradation.

FIGS. 4 and 5 depict charts useful for mix design to determinestructural strength of a mix.

FIGS. 6 and 7 depict charts useful for designing flexibility andstability properties by varying the ratio of blend sand and crushed fineaggregates in the mix.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENT

In developing my invention, I made the following observations anddiscoveries:

The nature and quality of the fine material aggregates passing the No. 4sieve essentially determine all behavioral qualities, e.g. durability,flexibility, compactibility workability, and stability of the blendedmixture because a change in its natural qualities affects air voids andeffective asphalt cement to a significantly greater extent than thecoarse aggregates.

Voidage can be mathematically computed with knowledge of the maximumconsolidation of the fine aggregates and asphalt cement which is basedupon the specific gravities, particle shape, and absorptioncharacteristics of all aggregates in the mixture.

The composition of fine aggregates supplied to a mixing plant can easilybe controlled within close tolerance as its segregation and degradationis neglible. Plant control can be effected by controlling the quantityof fines relative to the quantity of rock.

The nature and quality of the rock within the entire mixture determineonly the load bearing strength and rigidity of the pavement. Thecomposition, e.g. blend of different sized rock, does not have anysignificant effect of other qualities of the mixture.

The degradation and segregation of the rock supplied to a mixing plantcan be monitored and controlled within a high degree of accuracy therebyproviding effective gradation control at the mixing plant for producingmy uniform pavement.

The amount of air voids remaining in a compacted mixture can becontrolled by adjusting the proportion of the aggregates over a singlescreen size comparable to the No. 4 screen, by varying the quantity ofasphalt cement.

The flexibility and stability of an asphalt pavement mixture can becontrolled by varying the ratio of crushed fine aggregates to blend sand(river sand).

Stability can be increased by including crushed fine aggregates whichhave been subjected to extended crushing.

The best demarcation between coarse and fine aggregates for defininggradation and controlling the mix proportions at the mixing plant is asieve size approximating the No. 4 screen (0.187 inches or 4.75 mm.).

The mix proportions can be maintained at the mixing plant by separatelycontrolling and feeding controlled quantities of coarse aggregates andfine aggregates fed to the mixing plant. Blended aggregate samples arewithdrawn approximately every two hours, or as needed, and examined foraggregate gradation over a single sieve size, such as the No. 4 screen.Control of the blended mixture of aggregates over this single sieve sizeis obtained by regulating the feeding controls of the separate aggregatestorage bins to control the mixture over all sieve sizes of the job mixformula. A mixing plant having separate feeding controls and separatemonitoring means for the coarse and fine aggregates is disclosed in mycopending U.S. application Ser. No. 123,206 entitled Asphalt PavementMixing Plant Having Plural Weight Cells which was filed of even dateherewith. For support of appended claims, all essential matter disclosedtherein is incorporated herein by reference.

Based upon the foregoing observations and discoveries, I have discoveredan Index quantity herein called the Riguez Index to which graded blendsof aggregates are compared on a volumetric basis thereby to designmixes, analyze mixes, and control the mixing plant. The composition ofmy uniform pavement comprises aggregate mixtures within the followingmix proportions and possessing the natural aggregate qualities asdetermined by the indicated AASHTO test procedures; but are not limitedto these ranges:

    ______________________________________    Fine Aggregate    Bulk Specific Gravity                    2.676     (166.98#/CF)    Absorption      1.07%    Effective Specific Gravity                    2.705     (168.79#/CF)    Coarse Aggregate    Bulk Specific Gravity                    2.708     (168.98#/CF)    Absorption      1.84%    Effective Specific Gravity                    2.758     (172.10#/CF)    Asphalt Cement    Specific Gravity    (AR2000 Asphalt)                    1.0146    (63.31#/CF    Job Specifications:    Asphalt cement  5%        by weight    air void volume 5%        in compacted mixture    Fine Aggregate Blend    (% Passing)    no. 4           100%    no. 8           70%-85%    no. 16          46%-62%    no. 40          25%-40%   (not more than 7%                              passing no. 200)    Combined Fine and Coarse    Aggregate (% Passing)    3/4 inch           100%    1/2 inch           95%    3/8 inch        50%-60%    no. 4           44%-54%    no. 8           31%-45%    no. 16          20%-34%    no. 40          12%-22%    no. 200         2%-6%    ______________________________________

Natural variation in absorption and particle shape normally contributes2% to 5% error in designed air voidage. Natural variations in densitiesof aggregates normally fluctuate 5% to 15% for aggregates excavated froma single location. Since the quantity of asphalt cement injected in themixture is based upon total weight of aggregates, and that naturallyoccurring density variations fluctuate 5% to 15% for aggregatesexcavated at a single source; the quantity of effective asphalt cementin the mix varies to such a degree causing fluctuations in air voidageof ±10% or more, flexibility to fluctuate ±5 points or more, andstability to fluctuate by more than 1000 psi or more. These errors aretypical for aggregates generally used in asphalt pavement production.Occasionally, they are much worse due to radical changes in theformation of the rock at the site of excavation of the aggregates.

The worst errors though are brought about by the large tolerancesallowed in the job mix formula and job specifications that arepredesignated by the contracting authority. A typical gradationtolerance allowed between coarse and fine aggregate is 30% to 50%retained on No. 4 screen. It will be seen by the teachings of thisinvention that variations within that range could produce open gradedmixtures having more than 15% to 20% air voids, or a stability of morethan 1000 psi under a predesignated Marshall strength, or a flexibilitymore than 10 points below desired amount.

By using the techniques of my invention however, I am able to maintainair voidage, void filled, or voids in mineral aggregate (V.M.A.)constancy within less than 1/2% tolerance.

DERIVING THE RIGUEZ INDEX

The Riguez Index indicates the extent of compactibility of the mixture.It measures only the fines as the coarse rock does not compact. TheIndex, when periodically determined during production, measures naturalvariations in absorption, specific gravities, and particle shape of thefines thereby to allow the proper relationship between effective asphaltcement and aggregate to be maintained, and the air voidage to bemaintained. When making the volumetric comparison, only the absorptionand density of the aggregate are needed.

The Riquez Index is empirically derived by mixing and compacting amortar comprising a mixture of a representative sample only of the fineaggregate blending to be used in a job and the specified quantity ofasphalt cement. Mixing and compacting are performed by the Marshall orsimilar method which is described in the previously mentioned "MixDesign Methods for Asphalt Concrete and Other Hot Mixes" published bythe Asphalt Institute. Prior to compacting, the Marshall method providesfor heating and mixing the aggregates at 230 degrees Farenheit, plus orminus 10 degrees Farenheit, to ensure adequate homogenity of themixture. The compactive effort applied is equivalent to 75 blows with aten-pound hammer with an eighteen-inch drop on both sides of the hotmix, or an equivalent of 43,000 foot-pounds of pressure. Approximately1100 grams of the loose mixture is used to produce the specimen of about21/2 inches in height. After allowing the speciment to cool, the bulkdensity of this specimen is determined by weighing it in air todetermine weight, and measuring its displacement in water to determineits volume. Several specimens are made to assure accuracy. Thisprocedure can be completed within two hours.

The Riguez Index is computed by subtracting the known weight of asphaltcement from the bulk density of the speciment thereby to derive theweight of dry fine mineral agregate contained in a unit volume. RiquezValues O.D. (oven dried), defined herein as the WEIGHT OF THE DRY FINEMINERAL AGGREGATE PER CUBIC FOOT CONTAINED WITH ITS OWN VOLUME PLUS THEVOLUME OF EFFECTIVE ASPHALT CEMENT. A Riguez Index S.S.D. (saturatedsurface dried) and Riguez Values S.S.D. are used for mix design, mixanalysis and job control in my invention. They are determined by addingto the weight of dry aggregate per cubic foot, the weight of asphaltcement absorbed by the dry fine aggregate. The Riguez Index S.S.D. isherein called the Riguez Index.

Different blendings of fine aggregates or fine aggregates from differentsources have different characteristic Riguez Indexes. Thus any physicalproperty of the Riquez specimen can be used as job control parameter tobe monitored during production for producing uniform pavements ofsubstantial length from aggregates of differing natural qualities.

An average Riguez Index for the exemplary aggregates used herein wasdetermined as follows:

Bulk Density of Riquez Index specimens with 5% A.C. 2.247

Riguez Index computations: 2.247×62.4=140.21 lbs/CF×95%=133.20 lbs/C.F.O.D.

Absorption:

133.2 lbs×1.07%=1.42 lbs/166.98 lbs=0.85% in Volume

0.85%×63.31 lbs=0.54 lbs A.C.

Riquez Index SSD=133.2 lbs+0.54 lbs=133.74 lbs/C.F.

GENERATING VOLUMETRIC FUNCTIONAL RELATIONSHIPS

FIG. 1 depicts the volumetric behavior of aggregate blendings as afunction of proportion for my exemplary aggregates with the indicatedjob specifications. The curves are arithmetically computed usingrespective density values of rock and fines, respective absorptionvalues of the rock and fines, and the specific gravity of the asphaltcement. Specifically curve x represents the combined volume of the rockVCA, fines VFA, and effective asphalt cement VEAC as a function ofgradation. The difference between curve x and 100% value represents theeffective air voids VEA that will be contained in a blended mixture as afunction of gradation when the blended mixture is compacted with thesame compacted effort of the Riguez Index specimen. Curve x is derivedunder the assumption that only the mortar of fines are compacted andthat rock is incompressible. Curve v represents the combined volume ofthe rock VCA and fines VFA as a function of gradation. Curve zrepresents the volume only of the rock VCA as a function of gradation.Representations of aggregate behavior also can be made with quantity ofasphalt cement, rather than gradation, as the varible without departingfrom the spirit and scope of my invention.

The Riguez Value Curve depicted in FIG. 1 shows the relationship betweendensities of the mortar of the fine aggregate portion of the gradedmixture as a function of gradation and the density of the mortar of thefines of the Riguez Index specimen. For example, at the balance point(51.71% rock) indicated thereon, a unit volume of the mortar plusasphalt cement plus five percent air contains the same quantity of finesas a unit volume of the Riguez Index specimen. The gradation at whichthe balance point is reached is a function of the natural qualities ofthe aggregates. Thus only the fine aggregates of the mixture need bemonitored at the mixing plant. As soon as the natural qualities change,so does the balance point. Thus the mixing plant can be adjusted if achange in the Riguez specimen is noted during the operation of themixing plant. If the change is small, only the proportion is altered tocompensate for change in voidage. The quantity of asphalt cement alsocan be altered to correct for voidage changes resulting from changes inthe volume of the Riguez Index specimen. If the change is great, a newset of curves are computed to determine the new balance point of themixture for more accurate compensation of air voidage at the mixingplant. Since the Riguez Index in indicative of maximum consolidation ofthe fine particles, the Riguez Values show the extent consolidation ofparticles of the blended mixture including five percent air voids. TheRiguez Value curve indicates the percent error as the proportion movesaway from the balance point. It is seen that the Riguez Value curve isnearly constant with respect to gradation at the balance point. Thus arange within a few percentage points of the balance point is used forjob control at the mixing plant.

It is interesting to note that at some gradation greater the balancepoint, the Riguez Value curve intersects curve x. Experimentallyconducted tests shows the gradation at which the Riguez Value curveintersects curve x in the "bulking point" of the mixture. Thus, inaccordance with another aspect of my invention, the bulking point of ablended mixture can be arithmeticaly calculated. That information isuseful for establishing gradation limits or job mix formula limitationsfor mix design purposes. For the aggregate used herein, the theoreticalbulking point was empirically proven by laboratory test to be 85 poundsof rock per cubic foot or 58.8%.

To illustrate the exact procedure for computing the x, y, z, RiguezValue curves as a function of proportion, I performed step-by-stepcalculations at three proportion points on the gradation scale,beginning at and descending from the bulking point. As previouslyindicated, mixtures above the bulking point do not produce goodpavements as the air voids becomes uncontrollable. Accordingly, myanalysis is not use for aggregate mixtures above the bulking point.These computation can be performed by a digital computer. The graphicalpresentation resulting these curves is useful for controlling the mixingplant.

    __________________________________________________________________________    POINT A - CALCULATIONS OF VOLUMETRIC VALUES    OF MIX WITH 85# OF ROCK      85#/168.98#   CF Dry Rock        50.30%      Program 5% desired effectiver air                                       5.00%      Volume occupied by Rock plus 5% Effective Air                                       55.30%      Volume available for Fines plus Asphalt Cement (100 - 55.30)                                       44.70%      Dry Weight of Fines to 1 CF: 133.2# × 44.70%                                       59.54#      Combined Dry Weight of Aggregates 85# plus 59.54#                                       144.54#      Percentage Rock Dry Weight of Aggregate 85#/144.54#                                       58.80%      Total Weight of mix without absorption      factors 144.54#/95%              152.15#      Absorption:      85# × 1.84% = 1.56#/168.98#CF                                       0.92%      59.54# × 1.07% = 0.64#/166.98#CF                                       0.38%      Absorption on the basis of combination                                       1.30%    10.      Asphalt Cement Absorbed 1.30% × 63.31#C                                       0.82#      0.82#/152.15# = 0.54% on the basis of Total Mix.      0.54% × 95% = 0.51% on the basis of total aggregates.      Effective Asphalt Cement 5.00% - 0.51%                                       4.49%      Absorption values within a range of the gradation      scale will be practically the same. The analysis      from this point will be on the mixture with      absorption factors:      Volume of Rock 85# + 1.56# = 86.56#/172.10#                                       50.30%      Program 5% Effective Air         5.00%      Volume occupied by Rock plus 5% Effective Air                                       55.30%      Volume available for Fines plus A.C. (100% - 55.30)                                       44.70%      SSD Weight of Fines to 1CF = 133.74# × 44.70%                                       59.78#      SSD Weight of Aggregates 86.56# + 59.78#                                       146.34#    20.      Total Weight of Mixture 146.34#/100 - 4.49%                                       153.22#      Weight of Effective Asphalt Cement 153.22# - 146.34#                                       6.88#      Final Volumetric Analysis:      Total Weight                     153.22#      Effective Asphalt Cement         6.88#      SSD Weight of Aggregates         146.34#    SSD Wt. Rock 86.56#/172.10# =                       50.30% Volume of Rock    SSD Wt. Fines 59.78#/168.79# =                       35.42% Volume of Fines                       85.72% Volume of Aggr.      100 - 85.72% = 14.28% Voids in Mineral Aggregate      6.88# /63.31# = 10.87% Volume of Effective A.C.      3.41% Volume of Effective Voids      Percentage Voids Filled 10.87%/14.28%                                       76.12%      Calculated Voidless Mix 153.22#/100 - 3.41%                                       158.63#CF      Riguez Values 59.78#/35.42% plus 10.87%                                       129.14#CF      Riguez Value of original Index 129.14#/133.74#                                       96.56%    __________________________________________________________________________     POINT B - CALCULATIONS OF VOLUMETRIC VALUES    OF MIX WITH 80# ROCK    These calculations with identical values of Riguez Index,    Effective Air and Asphalt Cement, as were used for Point A.      80#/168.98# = CF Dry Rock        47.34%      Program 5% desired Effective Air 5.00%      Volume occupied by Rock plus Effective Air                                       52.34%      Volume available for Fines plus Asphalt Cement (100 - 52.34)                                       47.66%      Dry Weight of Fines to 1 CF 133.2# × 47.66%                                       63.48#      Combined Dry Weight of Aggregates 80# + 63.48#                                       143.48#      Percentage Rock Dry Weight of Aggregate 80#/143.48#                                       55.76%      Total Weight of mix without Absorption 143.48#/95%                                       151.03#      Absorption:      80# × 1.84% = 1.47#/168.98#CF                                       0.87%      63.48# × 1.07% = 0.68#/166.97#CF                                       0.41%      Absorption on the basis of combination                                       1.28%    10.      Asphalt Cement Absorbed 1.28% × 63.31#                                       0.81#      0.81#/151.03# = 0.54% on the basis of Total Mix.      0.54% × 95% = 0.51% on the basis of total aggregates.      Effective Asphalt Cement 5.00% - 0.51%                                       4.49%      Volume of Rock 80# + 1.47# = 81.47#/172.10#                                       47.34%      Program 5% Effective Air         5.00%      Volume occupied by Rock plus 5% Effective Air                                       52.34%      Volume available for Fines plus A.C. (100% - 53.34%)                                       47.66%      SSD Weight of Fines 133.74# × 47.66%                                       63.74#      SSD Weight of Aggregates 81.47# + 63.74#                                       145.21#    20.      Total Weight of Mix 145.21#/100% - 4.49%                                       152.04#      Weight of Effective Asphalt Cement 152.04# - 145.21#                                       6.83#      Final Volumetric Analysis:      Total Weight                     152.04#      Effective Asphalt Cement         6.83#      SSD Weight of Aggregates         145.21#    SSD Wt. Rock 81.47#/172.10#                     47.34% Volume of Rock    SSD Wt. Fines 63.74#/168.79#                     37.76% Volume of Fines                     85.10% Volume of Aggr.    100% - 85.10% =               14.90% Voids in Mineral Aggregates    6.83#/63.31# =               10.79% Volume of Asphalt Cement               4.11% Volume of Effective Voids      Percentage Voids Filled 10.79%/14.90%                                       72.42%      Calculated Voidless Mix 152.04#/100% - 4.11%                                       158.55#      Riguez Values 63.74#/37.76% - 10.79% =                                       131.29#      Riguez Value of original Index 131.29#/133.74                                       98.27%    __________________________________________________________________________     POINT C - CALCULATIONS OF VOLUMETRIC VALUES    OF MIX WITH 70# ROCK    These calculations with identical values of Riguez Index,    Effective Air and Asphalt as were used for Points A and B.      70#/168.98# = CF Dry Rock        41.43%      Program 5% Desired Effective Air 5.00%      Volume occupied by Rock plus 5% Effective Air                                       46.43%      Volume available for Fines plus Asphalt Cement (100 - 46.43)                                       53.57%      Dry Weight of Fines 133.2# × 53.57%                                       71.36#      Combined Dry Weight of Aggregates 70# + 71.36#                                       141.36#      Percentage Rock Dry Weight of Aggregate 70#/141.36#                                       49.52%      Total Weight of mix without Absorption 141.36#/95%                                       148.80#      Absorption:      70# × 1.84% = 1.29#/168.98#CF                                       0.76%      71.36# × 1.07#/166.98#CF   0.46%      Absorption on the basis of combination                                       1.22%    10.      Asphalt Cement Absorbed 1.22% × 63.31#                                       0.77#      0.77#/148.80# = 0.52% on the basis of Total Mix.      0.52% × 95% = 0.49% on the basis of total aggregates.      Effective Asphalt 5.00% - 0.49%  4.51%      Volume of Rock with Absorption 70# + 1.29# + 71.29#/172.10# =                                       41.43%      Program 5% Effective Air         5.00%      Volume occupied by Rock plus 5% Effective Air                                       46.43%      Volume available for Fines plus A.C. 100% - 46.43%)                                       53.57%      SSD Weight of Fines 133.74# × 53.57%                                       71.64#      SSD Weight of Aggregates 71.29# + 71.64#                                       142.93#    20.      Total Weight of Mix 142.93#/100% - 4.51%                                       149.68#      Effective Weight of Asphalt Cement 149.68# - 142.93#                                       6.75#      Final Volumetric Analysis:      Total Weight 149.68#      Weight of Effective Asphalt Cement  6.75#      SSD Weight of Aggregates 142.93#      SSD Wt. Rock 71.29#/172.10# 41.42% Volume of Rock      SSD Wt. Fines 71.64#/168.79# 42.44% Volume of Fines      83.86% Volume of Aggr.      100% - 83.86% = 16.14% Voids in Mineral Aggregates      6.75#/63.31# = 10.66% Volume of Effective A.C.      5.48% Volume of Effective Voids      Percentage Voids Filled 10.66%/16.14%                                       66.05%      Calculated Voidless Mix 149.68#/100% - 5.48%                                       158.35#      Riguez Values 71.64#/42.44% plus 10.66%                                       134.91#      Riguez Value of original Index 134.91#/133.74#                                       100.87%    __________________________________________________________________________     Some information about the physical properties of the mixture is readily     ascertainable as illustrated in the following Table 1. The balance point     information was derived by interpolation means. Total Vol. quantity     represents combined volume of aggregates and effective asphalt cement.

                  TABLE 1    ______________________________________    Calc.    Num-                       Point Balance    ber   Value       Point A  Point B                                      Point  C    ______________________________________    1     # Rock      85       80     73.48  70    7     % Rock      58.80    55.76  51.71  49.51    13    % Eff. A.C. 4.49     4.49   4.50   4.51    20    T.W. #'s    153.22   152.04 150.49 149.68    22    Vol % Rock  50.30    47.34  43.49  41.42    22    Vol % Fines 35.42    37.76  40.82  42.44    22*   Vol % Aggr. 85.72    85.10  84.31  83.86    22    % VMA(voids)                      14.28    14.90  15.69  16.14    22*   Vol Eff. A.C.                      10.87%   10.79% 10.69% 10.66%    22    % Eff. Voids                      3.41     4.11   5.00   5.48    *     Total Vol.  96.59    95.89  95.00  94.52    23    % Voids Fill                      76.12    72.42  68.13  66.05    --    70% Void Fill                      95.72    95.53  95.29  95.16    --    65% Void Fill                      95.00    94.74  94.51  94.36    26    Riguez Value                      96.56    98.27  100.00 100.87    ______________________________________

As used in this specification, the expression "#" means the unit ofweight "pound", and the expression "CF" or "C.F." means the unit ofvolume "cubic foot".

The Riguez Value curve of FIGS. 1 and 2 is derived from calculation 26of points A (96.56%), B (98.27%), and C (100.87%), which representsdifferent ratios between (a) the Riguez Value associated with therespective proportions of coarse and fines, and (b) the Riguez Index(133.74 pounds/cubic foot). The relationships for other proportions aregraphically derived by interconnecting points A, B, and C, as depictedin FIGS. 1 and 2. Calculation 25 is the Riguez Value expressed as theS.S.D. weight of fine aggregate per combined volumes of fine aggregateV_(FA) and effective asphalt cement V_(EAC). For example, calculation 25of point A expresses the Riguez Value as the S.S.D. weight of fineaggregate (59.78 pounds) which occupies the 35.42% (calculation 22) ofthe unit volume divided by the sum of its own volume (35.42%) and thevolume of the effective asphalt cement (10.87%), which equals 129.14pounds per cubic foot. Thus, the Riguez Value of a mixture of theproportion associated with point A equals the ratio of 129.14/133.74, or96.56 % of the original Riguez Index. Similar calculations areillustrated for points B and C.

At the "Balance Point", the Riguez Value equals the Riguez Index, aspreviously indicated. FIG. 2 shows that the Balance Point is attained ata proportion, or gradation of coarse and fine aggregates, of 51.71%coarse aggregate and 48.31% fine aggregate; which implies that theamount of fines contained in a volume constituted by the fine aggregateand effective asphalt of a Balance Point mixture equals 133.74 poundsper cubic foot. This is the same quantity of fines contained in a unitvolume of the Riguez Index specimen. Accordingly, a mixture of suchproportion possesses the Balance Point parameters depicted in Table 1,one of which being 5% effective air void volume V_(EAC), which I soughtto achieve.

CONTROL OF VOIDAGE AT THE MIXING PLANT

The voidage of a blended mixture having a balance point proportioncontains the specified amount of air. To maintain continuity, I nowexplain how the voidage of the mixture can be accurately controlled byvarying the quantity of asphalt cement or by varying the gradation overthe No. 4 or similar size screen. As used in this specification andclaims, "gradation" , "gradation index", and "proportion" mean thepercent of coarse aggregate retained on the No. 4 or similar size sieveand is expressed in relation to the total dry weight of all aggregatesin the mixture.

FIG. 2 shows an expanded portion of FIG. 1 near the balance point andsets forth the 65% and 70% voids filled isograms and a series of asphaltcement isograms ranging from 4.4% to 5.6% by weight asphalt cement.Using this chart, percent voids filled or percent effect air voids canbe controlled by varying proportion or quantity of asphalt cement toproduce a uniform pavement. Conversely, to analyze any mixture ofaggregates and asphalt cement, the percent voids filled and the percenteffective air voids and be readily ascertained by measuring itsproportion over the No. 4 sieve and locating the corresponding point onthe chart of FIG. 2.

To illustrate a typical plant control use, assume that it is desired toalter an asphalt mixture of our exemplary aggregates from the balancepoint to a mixture having 70% voids filled at the specified five percentby weight asphalt cement. The gradation of the mix at the plant wouldthen be increased to 53.4% (the intersection of the 5% asphalt cementisogram and the 70% voids filled isogram). At the gradation of 53.4%,air void volume is readily ascertained as approximately 4.6%. If a 65%void fill value is desired, the gradation would be decreased to 48.8%and the air void volume changes to 5.6%. With the use of the asphaltcement isograms, the air void volume and the percentage of voids filledcan be systematically and accurately controlled without the need toperform extended laboratory tests and analytical procedures now requiredin the paving industry.

To illustrate another use of the chart of FIG. 2, the percentage airvoids also can be altered at a fixed gradation by varying the quantityof asphalt cement. For example, suppose that it is desired to maintain agradation of 50%. It is readily seen that the mixture will contain 5.5%air voids at five percent by weight asphalt cement. By increasing thequantity of asphalt cement to 5.4% by weight, the air voids willdecrease to approximately 4.4%. Any quantity of air voids can beobtained merely by interpolation between the asphalt cement isogramsdepicted in FIG. 2. Thus it now is apparent that a paving contractor cannow alter his mix within the predesignated job specifications to achieveuniformity in the pavement. Likewise, the contracting authority can nowaccurately specify the optimum job specifications merely by examiningthe fine aggregates to be used in the job and with specific gravityvalue and absorption value of aggregates. Similarly, the paving engineercan design the mix within given job specification to produce a pavementhaving predesignated physical parameters with the same knowledge aboutthe aggregate qualities.

FIG. 3 depicts density of the aggregate mixture as a function ofgradation. Simply by using density of the compacted mixture at thelaydown site as a job control parameter, the voidage parameters of themixture can readily be ascertained upon correlation with the graph ofFIG. 3. Of course, any parameter of the mixture that varies as functionof gradation or effective asphalt cement can be selected as a jobcontrol parameter. The best job control parameters are those of theRiguez specimen as produced from the fine aggregate samples withdrawnfrom the mixing plant. The job control engineer may use voidage asdetermined by conventional testing methods as a job control parameter,but then the advantage of prompt results as provided by the Riguezspecimen or other measurements for plant control purposes is sacrificed.

As previously indicated, aggregates which are supplied to the pavingplant can simply be controlled over a single screen size, such as theNo. 4 screen, for controlling mix proportions the mixture. Instead ofusing the chart of FIG. 2, other graphical parametric representationsand comparisons of the mixture against the Riguez specimen can be used.It would be impractical however to present all such representations formix design, mix analysis, or job control methods so the illustrationspresented herein should be construed as illustrative, rather than as alimitation.

FLEXIBILITY AND STABILITY MIX DESIGN PROCEDURES

The degree of flexibility and stability of a compacted mixture can bedesigned by determining their respective values as a function of theratio of crushed fine aggregate to blend sand in the mixture. Theoptimum proportion for voidage control of the blended mixture of fineaggregate and coarse aggregate can be determined by use of the RiguezIndex method described method. The blending ratio of crushed fines toblend said determines stability and flexibility. Once designing theproper blend of fines, plant control also can be effected by the methodset forth above. Accordingly, my uniform pavement also can be producedto be uniform both in flexibility and stability. Furthermore, once theflexibility and stability functions are determined, any mixture ofaggregates deviating from the specific ratio of crushed fines to blendsand can be adjusted in accordance with predetermined relationships.

Now, in designing a mixture having the desired flexibility and stabilityproperties, I noted that with the use of the aggregates on hand,stability is increased as the percentage of crushed aggregate isincreased and that flexibility (of flow) is increased as the percentageof asphalt cement is increased. These are two very importantobservations because now, a mix design engineer may proceed directly tothe appropriate combination of crushed fines and blend sand to achievethe desired flexibility and stability. The procedure accordingly removesall guess work and trial-and-error which previously exists in mix designpractice. Flow and stability are inversely proportional, however, bothvalues may be achieved by increasing the extent of crushing of thecrushed fine to produce greater stability for a given flexibility. Isuggest crushed limestone to provide increased stability.

I have prepared in FIG. 6 a Riguez Value function for each of the sevendifferent blends of crushed fines and blend sand (river sand). Curves 2and 3 are examined at a gradation of 57.0% (Point a) and 55.4% (Pointb), respectively. Both mixes have 5% asphalt cement, but the mix ofPoint (a) has 48.10% crushed fines and the mix of Point (b) has 57.45%crushed fines. Actual mixes at the selected gradation points wereprepared. The mix of curve 2 had a stability of 3200 and flexibility of5, while the mix of curve 3 had a stability of 2400 and flexibility of10. Thus, it is seen that flexibility can be increased by adding morecrushed fines in the blend of fine aggregate without changing thequantity of asphalt cement.

In examination of actual mixtures prepared at fine aggregate blends ofcurves 5 and 6 of FIG. 6, I note that at Point (d) and Point (f),stabilities of the samples were 3116 and 2590, respectively, andflexibilities were 9 and 9.5, respectively. Thus, flexibility can beincreased by increasing the amount of asphalt cement. It also isinteresting to note that for a higher percentage of crushed aggregatewith the quantity of asphalt cement held constant the stabilityincreased to 3150 and flow decreased to 8.5 (Point e); and that at alower percentage of crushed aggregate with the quantity of asphaltcement held constant the stability decreased to 2243 and flow increasedto 13 (Point c). This observation can be used generally to ascertain theappropriate combination blend sand, crushed fine aggregate and asphaltcement to design a mix having any degree of flexibility, stability, airvoidage or other desired property.

Further, I have been able to achieve mixes having a stability exceeding3000 under the Marshall standards with flexibility values between 8 and16. Present methods permit at best may achieve flexibility of 5 to 8 forstabilities over 2000 psi under Marshall standards. Controlled stabilityand flexibility of my illustrated magnitudes have never been attainableby prior art methods.

FIGS. 4 and 5 show how the Riguez Index and total volume of the mixturevaries according the ratio of blend sand to crushed fines. The specificratios are indicated in the corresponding examples set forth below. Itis seen, from FIG. 5 that the Riguez Index increases as the amount ofcrushed fines in the total mix increases. Thus a more dense mix withincrease structural strength having a greater stability is attained withincreased crushed fines.

For seven different combinations of crushed fines and blend sand, I showhow the Riguez Index changes in FIG. 5. In FIG. 6, I show the volumeticcomparisons as a function of gradation for each of the differentcombinations. I have produced several samples of mixtures within theconstraints indicated on the curves for illustrating the variation ofphysical properties of the mix and thereby provide the means to guidethe design engineer directly to the desire mixture for achievingpredesignated physical properties without any guess work ortrial-and-error process whatsoever. Several gradation points of some ofthe curves were selected to have mix parameters within a predesignatedjob specification (such as percent asphalt cement--5%, 5.5% percentageair voids 4%-5%, voids in mineral aggregate 15%-16%) and a mixture ofthe indicated blends were physically prepared. The physical parametersof some of the mixtures are tabulated below.

    ______________________________________    Curve 1    ______________________________________    Total Mix    Coarse Rock      60%    Crushed Fines    15%    Blend Sand       25%    % Crushed Fines  39.76    Bulk density of Fines                     135.58    lbs/cubic foot    Riguez Index     129.20    Sp. Gravity Fines (SSD)                     2.7763    Bulk Density Total Mix                     154.50    % Retained no. 4 screen                     58.50    % Asphalt Cement 5.0    Volume of Rock   47.12%    Volume of Fines  36.40%    V.M.A.           16.48%    Effective Air Voids                     5.12%    Voidless Mix     162.84    Riguez Value     101.6    ______________________________________    Curve 2    ______________________________________    Total Mix    Coarse Rock      59%    Crushed Fines    19%    Blend Sand       22%    % Crushed Fines  48.10    Bulk density of Fines                     137.32    lbs/cubic foot    Riguez Index     130.87    Sp. Gravity Fines (SSD)                     2.7793    Bulk Density Total Mix                     157.70    % Retained no. 4 screen                     57.00    % Asphalt Cement 5.0    Volume of Rock   48.01%    Volume of Fines  36.82%    V.M.A.           15.17%    Effective Air Voids                     3.54%    Voidless Mix     163.49    Riguez Value     101.0    ______________________________________    Curve 3    ______________________________________    Total Mix    Coarse Rock      45%    Crushed Fines    36%    Blend Sand       19%    % Crushed Fines  57.45    Bulk density of Fines                     141.89    lbs/cubic foot    Riguez Index     135.27    Sp. Gravity Fines (SSD)                     2.7989    Bulk Density Total Mix                     156.40    % Retained no. 4 screen                     55.40    % Asphalt Cement 5.0    Volume of Rock   46.23%    Volume of Fines  37.68%    V.M.A.           16.09%    Effective Air Voids                     4.45%    Voidless Mix     163.68    Riguez Value     98.85    ______________________________________    Curve 4    ______________________________________    Total Mix    Coarse Rock      37%    Crushed Fines    42%    Blend Sand       21%    % Crushed Fines  58.33    Bulk density of Fines                     143.13    lbs/cubic foot    Riguez Index     135.90    Sp. Gravity Fines (SSD)                     2.8003    Bulk Density Total Mix                     155.20    % Retained no. 4 screen                     49.60    % Asphalt Cement 5.5    Volume of Rock   40.86%    Volume of Fines  42.11    V.M.A.           17.03%    Effective Air Voids                     4.35%    Voidless Mix     162.26    Riguez Value     98.82    ______________________________________    Curve 5    ______________________________________    Total Mix    Coarse Rock      40%    Crushed Fines    44%    Blend Sand       16%    % Crushed Fines  71.16    Bulk density of Fines                     149.49    lbs/cubic foot    Riguez Index     142.97    Sp. Gravity Fines (SSD)                     2.8253    Bulk Density Total Mix                     156.90    % Retained no. 4 screen                     44.50    % Asphalt Cement 5.0    Volume of Rock   37.20%    Volume of Fines  46.78%    V.M.A.           16.02%    Effective Air Voids                     4.41%    Voidless Mix     164.14    Riguez Value     98.90    ______________________________________    Curve 6    ______________________________________    Total Mix    Coarse Rock      41%    Crushed Fines    42%    Blend Sand       17%    % Crushed Fines  69.30    Bulk density of Fines                     148.15    lbs/cubic foot    Riguez Index     140.52    Sp. Gravity Fines (SSD)                     2.8242    Bulk Density Total Mix                     156.12    % Retained no. 4 screen                     44.60    % Asphalt Cement 5.5    Volume of Rock   36.96%    Volume of Fines  46.21%    V.M.A.           16.83%    Effective Air Voids                     4.02%    Voidless Mix     162.66    Riguez Value     98.20    ______________________________________    Curve 7    ______________________________________    Total Mix    Coarse Rock      23%    Crushed Fines    62%    Blend Sand       15%    % Crushed Fines  75.92    Bulk density of Fines                     152.37    lbs/cubic foot    Riguez Index     144.54    Sp. Gravity Fines (SSD)                     2.8369    Bulk Density Total Mix                     156.50    % Retained no. 4 screen                     37.70    % Asphalt Cement 5.5    Volume of Rock   31.32%    Volume of Fines  51.96%    V.M.A.           16.72%    Effective Air Voids                     3.90%    Voidless Mix     162.85    Riguez Value     98.24    ______________________________________

FRICTION OVERLAYS USING RIGUEZ, STABILITY, & FLEXIBILITY DESIGNPROCEDURES

A friction course for covering existing asphalt or portland cementconcrete surfaces also can be produced using the teachings of thisinvention. As previously indicated, prior art friction courses comprisesopen graded mixtures which subjected the asphalt cement to waterstripping and aeration. A friction surface is established by the cornersand edges of the aggregated protruding upwardly of the riding surface. Alow voidage dense graded friction course is preferred, but production ofsuch mixes having high stability and flexibility have previously beenimpossible. Aggregate particles of prior art friction surface tend toreorientate or submerge into the underlying pavement, particularly whenheated or subjected to impact forces, thereby losing their frictionproperties immediately after load applications. Friction courses ofsmaller particles are more susceptable to loss of friction qualitybecause usual level of displacement and reorientation occuring with thepermissable wide mix tolerances generally given to paving contractors.Using the above teachings however, a uniform low voidage high strengthand highly flexible dense graded friction course can now be producedusing aggregates of any size because the stability, flexibility, and airvoidage can be accurately designed in the laboratory and controlled atthe mixing plant. Friction overlays using top size aggregates as smallas one-fourth inch or one-half inch can now be produced. Such pavementshave superior life and frictional qualities and can be revitalizeddecades after initial laying by typical emulsions or reclamite withoutstripping the asphalt cement from the aggregates.

Any overlay requires the overlay thickness to be at least twice thediameter of the largest particle. Since I now may use smaller particlesfor my friction overlay, I can produce a thin overlay, such as one-halfto one inch thick thus resulting in substantial cost saving inproduction and consumption of asphalt cement.

To establish mix design for friction overlays, it only is necessary toselect the top screen aggregate size which renders the desired friction.Of course, larger crushed particles provide greater frictional qualitiesthan smaller crushed particles. I provide a top size screen for crushedparticles of three-fourth inch, one-half inch, three-eights inch, or theNo. 4 screen. For highway application, the one-half inch top size screenis recommended. Airport landing and runway pavements require anti-skidfrictional qualities depending on the size, speed, and weight of landingaircraft operating from the airfield. For landing speeds exceeding 140knots for heavy jet aircraft, high impact resistence, stability, andfriction is desirable at the point of landing and throughout the entirelength of the runway for skid control and breaking. Flexibilityexceeding 12 or 14 and stability exceeding 2500 or 3000 under Marshallstandards can be designed and produced, as indicated above. Separationof the pavment material must be minimized to prevent flying debris upontakeoff and landing.

In any friction course, the quantity of mineral filler passing the No.200 screen should be limited to eight percent maximum. Five percent tosix percent is ideal. The proportion of blend sand should be selected togive the desire flexibility and stability for the overlay frictionsurface. Air voids should be minimized to two percent to three percentto minimize aeration and water seepage and to protect the underlaysurface, flexibility should be designed between 8 and 16, and stabilityshould be between 2000 and 3000 psi under the Marshall standards.Accordingly, the designer of a friction overlay should first identifythe top screen size to select level of friction desired, then performthe flexibility and stability design procedure set forth above to selectthe desired mix proportions (noting that increased crushed finesincreases stability and increased asphalt cement increases flexibility),and then perform the volumetric analysis to achieve voidage generallybetween 2% and 3%.

This disclosure reveals the technical aspects of the Riguez Index methodof design and stability and flexibility design. It is both a designmethod and control method and selects a particular gradation ofaggregates or quantity of asphalt cement to render voidage values forproducing uniform pavements. Thus substantial cost savings inconstruction are accorded. Further, the time required to perform theanalysis and to ascertain corrective action at the mixing plant are muchshorter so that results can be obtained in a few hours, instead ofweeks. The principal design and control methods for selecting selectproper combinations of aggregates are very easy to execute in the fieldand in the laboratory. The teachings of this invention will allow pavingcontractors to design their mixes, evaluate better sources ofaggregates, give exact bids, and, more important, to have a verymeaningful understanding of the proper design of their product by theirown forces and control.

It will now be apparent to those skilled in the art from the aboveteachings that substantial uniform pavement areas can be produced by mixdesign, mix analysis, and job control methods other than thosespecifically indicated in my disclosure. My inventions includes theproduct and the processes disclosed as well as those products andprocesses that come within the scope of any modifications, adaptations,or extensions of the above teachings.

I claim:
 1. An asphalt pavement structure of substantial area havingsubstantially constant volume V_(EA) of air voids under a standardcompaction, said pavement comprising asphalt cement and a mixture of acoarse aggregate blending and a fine aggregate blending, the aggregatesof said fine aggregate blending being variable in absorption, specificgravity, particle shape, size distribution, or consolidation under saidstandard compaction, and wherein the proportion of said coarse and fineaggregate blending is below the bulking point of the mixture, saidproportion being periodically determined during the production of saidpavement by the steps of:A. demarcating the aggregates to define coarseand fine aggregates, B. mixing a reference sample including said fineaggregate and a quantity of asphalt cement, C. compacting said referencesample under said standard compaction, D. determining an Index quantitythat represents the quantity of fine aggregate per unit volume of saidreference sample compacted under said standard compaction, and E.selecting a proportion of coarse and fine aggregates according to saidvolumetric relationship:

    V.sub.CA +V.sub.FA +V.sub.EA +V.sub.EAC =1 unit volume

for differing proportions of coarse and fine aggregate, wherein thequantity of fine aggregates per unit of the combined volumes V_(FA) andV_(EAC) substantially equals said Index quantity, where V_(EAC) is thevolume effective asphalt cement, V_(CA) is the volume of the coarseaggregate, and V_(FA) is the solid voidless volume of the fineaggregate.
 2. An asphalt pavement structure as recited in claim 1wherein said constant volume of air voids is substantially constantconstant between 2% and 5% by volume under said standard compaction. 3.An asphalt pavement structure as recited in claim 2 wherein said fineaggregate blending comprises 30% to 100% by weight of crushed finemineral aggregate, and 0% to 70% by weight of mineral aggregate from anatural fine mineral aggregate source.
 4. An asphalt pavement structureas recited in claim 3 wherein the crushed fine aggregate comprisescrushed limestone and the natural fine aggregate comprises sand.
 5. Anasphalt pavement structure as recited in claim 3 wherein 100% by of theaggregates of said fine aggregate blending passes the No. 4 screen and2% to 8% by weight of the dry aggregates pass the No. 200 screen.
 6. Anasphalt pavement structure as recited in claim 5 wherein the fineaggregate blending comprises the job mix formula:100% passes No. 4screen 70% to 85% passes No. 8 screen 46% to 62% passes No. 16 screen25% to 40% passes No. 40 screen 2% to 8% passes No. 200 screen
 7. Ahighly stable dense graded asphalt friction overlay of substantial areafor covering a pavement surface, said overlay containing less than 3.5%by volume of air voids V_(EA) under a standard compaction and having aMarshall stability exceeding 1800 psi with a Marshall flexibilitybetween 8 and 16, said friction overlay comprising asphalt cement and amixture of a coarse aggregate blending and a fine aggregate blending,the aggregates of said fine aggregate blending being variable inabsorption, specific gravity, particle shape, size distribution, orconsolidation under a standard compaction, and wherein the proportion ofsaid coarse and fine aggregate blending is below the bulking point ofthe mixture, said proportion being periodically determined during theproduction of said friction overlay by the steps of:A. demarcating theaggregates to define coarse and fine aggregates, B. mixing a referencesample including said fine aggregate and a quantity of asphalt cement,C. compacting said reference sample under said standard compaction, D.determining an Index quantity that represents the quantity of fineaggregate per unit volume of said reference sample compacted under saidstandard compaction, and E. selecting a proportion of coarse and fineaggregates according to said volumetric relationship:

    V.sub.CA +V.sub.FA +V.sub.EA +V.sub.EAC =1 unit volume

for differing proportions of coarse and fine aggregate, wherein thequantity of fine aggregate per unit of the combined volumes V_(FA) andV_(EAC) substantially equals said Index quantity, where V_(EAC) is thevolume effective asphalt cement, V_(CA) is the volume of the coarseaggregate, and V_(FA) is the volume of the fine aggregate.
 8. A frictionoverlay as recited in claim 7 wherein said standard compaction is acompactive effort as defined by the Marshall method.
 9. A frictionoverlay as recited in claim 7 wherein at least 50% of the fineaggregates comprise crushed mineral aggregate.
 10. A friction overlay asrecited in claim 7 wherein the top size of the coarse aggregates is lessthan one inch mean diameter and greater than the No. 4 sieve.
 11. Afriction overlay as recited in claim 7 having uniform body wherein thesize of substantially all of the coarse aggregates therein are closelygraded, the median size of said closely graded coarse aggregate beingwithin the range of one inch mean diameter and the No. 4 sieve.
 12. Afriction overlay as recited in claim 7 having an air void volumetolerance within 1/2% within said range of less than 3.5%.
 13. Anasphalt pavement as recited in claim 3 having an air void volumetolerance within 1/2% within said range of 2% to 5%.
 14. An asphaltpavement as recited in claim 3 wherein said standard compaction is acompactive effort as defined by the Marshall Method.
 15. A compactedasphalt paving composition containing a predetermined air void volumeV_(EA) under a standard compaction; said composition comprising amixture of coarse aggregate, fine aggregate, and asphalt cement; therespective proportions of coare aggregate, fine aggregate, and asphaltcement being determined by the steps of:A. demarcating the aggregates todefine coarse and fine aggregates, B. mixing a reference sampleincluding said fine aggregate and a quantity of asphalt cement, C.compacting said reference sample under said standard compaction, D.determining an Index quantity that represents the quantity of fineaggregate per unit volume of said reference sample compacted under saidstandard compaction, and E. selecting a proportion of coarse and fineaggregates according to said volumetric relationship:

    V.sub.CA +V.sub.FA +V.sub.EA +V.sub.EAC =1 unit volume

for differing proportions of coarse and fine aggregates, wherein thequantity of fine agregates per unit of the combined volumes V_(FA) andV_(EAC) substantially equals said Index quantity, where V_(EAC) is thevolume effective asphalt cement, V_(CA) is the volume of the coarseaggregate, and V_(FA) is the volume of the fine aggregate.
 16. Acomposition as recited in claim 15 wherein said coarse aggregate andfine aggregate are demarcated by the No. 4 aggregate sieve.
 17. Acomposition as recited in claim 16 wherein said standard compaction is acompactive effort as defined by the Marshall method.
 18. An asphaltsurface of substantial area having a substantially constant volumeV_(EA) of air voids under a standard of compaction according to theMarshall method of compaction, said pavement comprising asphalt cementand a mixture of a coarse aggregate blending and a fine aggregateblending, the aggregates of said fine aggregate blending being variablein absorption, specific gravity, particle shape, size distribution, orconsolidation, and wherein the proportion of coarse and fine aggregateblending is below the bulking point of the mixture, said proportion ofcoarse and fine aggregates being periodically determined during theproduction of said asphalt surface by the steps of:A. demarcating theaggregates by a sieve size approximating the No. 4 sieve to definecoarse and fine aggregates, B. mixing a reference sample including saidfine aggregate and a quantity of asphalt cement, C. compacting saidreference sample according to the Marshall method of compaction, D.determining an Index quantity that equals the weight of fine aggregateper unit volume of said reference sample compacted under the Marshallmethod of compaction, and E. selecting a proportion of coarse and fineaggregates according to said volumetric relationship:

    V.sub.CA +V.sub.FA +V.sub.EA +V.sub.EAC =1 unit volume

for differing proportions of coarse and fine aggregate, wherein theweight of fine aggregates per unit of the combined volumes V_(FA) andV_(EAC) substantially equals said Index quantity, where V_(EAC) is thevolume effective asphalt cement, V_(CA) is the volume of the coarseaggregate, and V_(FA) is the volume of the fine aggregate.